Atomic resonators, e.g. cesium resonators, are used because of the precision of their atomic transition defining a standard frequency that is exact and very stable. In apparatus designed for this purpose, a driver signal is synthesized at the resonant frequency of the resonator, it is delivered in modulated form to the resonator, and the response signal of the resonator is picked up and demodulated, with the frequency of a first oscillator then being servo-controlled on the basis of the demodulated signal. Such apparatus enables a standard signal to be generated having frequency which is very exact and very stable, to within about 10−12 and 10−14, respectively.
Such apparatuses are required, for example, in space applications, for navigation by satellite.
U.S. Pat. No. 5,148,122 describes apparatus of the kind described above, for a cesium resonator comprising:                a first oscillator at 10 megahertz (MHz) suitable for producing a first signal at a frequency which is a function of the response signal from the resonator;        a second oscillator producing a second signal at 650 MHz as a function of a control signal;        means for servo-controlling the phase of the second signal on the first signal, producing the control signal; and        means for generating the reference signal and the driver signal downstream from the second oscillator, which means include frequency dividers and multipliers.        
That apparatus turns out to present drawbacks. It requires a large number of component elements, thereby making it complex, heavy, and voluminous. It consumes a large quantity of energy and it is expensive.
The document entitled “A new RF architecture for cesium frequency standards”, published in pp. 134 to 142 of 1992 IEEE Frequency Control Symposium, discloses similar apparatus further comprising a third oscillator downstream from the multiplier and divider circuit and producing the driver signal at the resonant frequency.
Of even greater complexity, that apparatus additionally creates disturbance by electromagnetic radiation, and the atomic resonator is sensitive thereto, because an oscillator is being used at its resonant frequency. Overcoming such disturbance requires shielding, which is expensive, heavy, and bulky.
The document entitled “Cs frequency synthesis: a new approach”, published on pp. 615 to 619 of Volume 2 of 1999 Joint Meeting EFTF—IEEE IFCS, describes a cesium resonator frequency synthesizer having oscillators at 5 MHz, 100 MHz, and 6.4 gigahertz (GHz). An analog regenerator divider responds to the oscillator at 6.4 GHz to generate signals at 3.2 GHz and 9.6 GHz. A signal at 9.192 GHz for the cesium resonator is generated after mixing a signal at 407.368 MHz with the signal at 9.6 GHz.
That synthesizer likewise comprises a large number of circuits including an analog regenerator divider which must be made specially for the synthesizer.